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Crawlers, Dozers, Loaders & Backhoes Discussion Forum

JCB 3C MK11 Trans

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Bob in Mi.

10-28-2007 20:28:37




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I have a 3c mk11 with a shuttle trans and works most of the time. You will be driving along and suddenly will lose speed and stop. It is like pump has lost it's prime. Let set for couple minutes and rev motor and most of the time trans pressure will return and you can take off again. Can anyone help with experience with JCB. Thanks




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AJ.

10-31-2007 02:09:49




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 Re: JCB 3C MK11 Trans in reply to Bob in Mi., 10-28-2007 20:28:37  
That would be a TC machine and it would be 30 years old,they were a very short run and the last JCB built on a ag tractor(Nuffield with Leyland 3.8 engine)all JCBs after that model were built on a purpose built backhoe chassis,your problem tends to make be think that the oil pressure is interupted,put the loader up and secure it,look at the left side of the engine inside the frame and you will see the pump for the PS and the charge pump for the tc and shuttle,the back section of the pump is for the tc/shuttle,it has three pipes attached to that section,one suction,one pressure and the one on the back is for the pressure relief valve,looking at the back of that pump you will see a dome nut,under that nut is the relief valve,its got a spring and some shims,remove it an check the valve and seat for any dirt or jamming,if it ok put it back,look on the pressure line it may have a pressure test quick break fitting to attach a pressure gauge,I am a bit rusty now on the specs as I am involved in the repair business and don"t see many machines that are over 5 years old,maybe the dealer has them,JCB changed their models in that era often,it is either the relief valve,drawing air,restricted oil flow or blocked breathers causing a vacuum but the clutches and TC will be ok once it working strong till it stalls.I can"t remember if that had a nudge pedal or not if it has make sure its free and not sticking,do the simple things like the breather and see how it goes.
AJ
UK

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Bob in Mi

10-31-2007 09:49:46




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 Re: JCB 3C MK11 Trans in reply to AJ., 10-31-2007 02:09:49  
AJ,

This unit was built in the mid 1970's. No nudge pedal ( here we call them inching pedals). I looked to see the dome nut but could not without lifting bucket, battery is down so I did not start it. Just to make sure you and I are on the same page. This unit is what most refer to as a white cab, being the later, earlier being yellow. Backhoe slides from side to side and leveling feet go straight down.

When this unit is running and warmed up the tran pressure runs about at the 150 ( 10 kg) psi mark, when reved up, a little higher, but not much. Needle does hold steady. WHen it loses pressure and the needle drops to zero I sit letting it idle and after 2-3 minutes I can rev the motor up a little and the pressure will normally climb back up, needle jumping a bit and then sit at the 150 psi again. Over the time that I have had the unit it loses pressure when I am shifting from one direction to another, this being when I lift off the throttle, shift the shuttle and then get back on the throttle. Only other times are when I don"t let the unit warm up completely and normally when you take off the pressure needle is flucuating heavily and will lose pressure, let it set, rev it up a few times and the pressure comes back.

Tomorrow I will charge the battery and get the bucket up and secured and check the relief valve. The alternator is not working and I called the dealer for a new one, after they got done laughing they said they will check and see if the can get one. Thanks again for your help, I do have a manual about 3 inches thick and it should have the spec's for pressure. Bob

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AJ.

10-31-2007 12:07:30




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 Re: JCB 3C MK11 Trans in reply to Bob in Mi, 10-31-2007 09:49:46  
Told you to look on the wrong side of the engine it should be the right sitting in the seat,it is handy having the gauge at least is is narrowing things down,when you get the bucket up have a look at the valve,when you have the valve and spring out and any shims,screw the cap on and nip it up,start the engine and put it in drive,doing this would move any small grit away from the valve area and it would get trapped in the filter,it must be some small like the valve sticking open.
AJ

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AJ.

10-29-2007 02:02:45




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 Re: JCB 3C MK11 Trans in reply to Bob in Mi., 10-28-2007 20:28:37  
Two types of the 3C,first with a shuttle and was known as a TC machine,it had shuttle shift coupled to a two lever gearbox,the later type was called a Powertrain and had a Borg Warner shuttle coupled to a one lever four speed gearbox,the TC charge pump is external,it is mounted on the back of the power steering pump on the right hand side of the engine,the Powertrain charge pump is an integral part of the shuttle and to change it the shuttle has to be removed,in either case look round the top of the shuttle housings and find the breather,remove and clean them,if you have no joy after that come back with what machine you have and don"t bother with any serial numbers as I have no reference on what would be in what,there could be a suction strainer blocked or the pick up line is drawing air.
AJ

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Bob in Mi

10-30-2007 14:06:52




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 Re: JCB 3C MK11 Trans in reply to AJ., 10-29-2007 02:02:45  
Nice to find someone that remembers these old units. This has a single shift lever and shuttle handle left side of steering wheel. I have cleaned the bell shaped filter under seat. Changed trans fluid a couple years back and replace the filter cartridge and replace fluid with JCB special trans fluid from JCB dealer. No change. I bought this unit 6 years ago, at an auction. It was as is, where it is, type of thing. Have been to the JCB dealer but the machine is older than the mechanics. So any help is greatly appreciated. Thanks, Bob.

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